1. Field of the Invention
The present invention relates to a focus adjustment apparatus and a focus adjustment method and, more particularly, to a focus adjustment apparatus, a focus adjustment method, and an imaging apparatus for performing a focus adjustment by using pixel signals based on rays of object light which pass through different exit pupils of a focusing optical system.
2. Description of the Related Art
As one of focus adjustment methods of an imaging apparatus, there is an imaging plane phase difference method of performing a focus detection of a phase difference method by focus detection pixels formed on an imaging element. In a focus adjustment of the imaging plane phase difference method, a defocus direction and a defocus amount can be simultaneously detected by the focus detection pixels formed on the imaging element and the focus adjustment can be performed at a high speed.
For example, U.S. Pat. No. 4,410,804 discloses an imaging apparatus using a two-dimensional imaging element in which one microlens and a plurality of divided photoelectric conversion units are formed with respect to one pixel. The divided photoelectric conversion units are constructed so as to receive rays of light which pass through different areas of an exit pupil of a photographing lens through one microlens, and attain a pupil division. An image shift amount is obtained from focus detection signals received by the divided photoelectric conversion units (focus detection pixels) and a focus detection of a phase difference method can be performed. Japanese Patent Application Laid-Open No. 2001-083407 discloses such a technique that an image pickup signal is generated by adding focus detection signals received by the divided photoelectric conversion units.
Japanese Patent Application Laid-Open No. 2000-156823 discloses such an imaging apparatus that a pair of focus detection pixels are partially arranged on an imaging plane of a two-dimensional imaging element constructed by a plurality of image pickup pixels. In such an imaging apparatus, the pupil division is attained by constructing one pair of focus detection pixels in such a manner that rays of object light which pass through different areas of an exit pupil of a photographing lens is received by a light shielding layer having an aperture portion. There has also been disclosed such a technique that image pickup signals are obtained by the image pickup pixels arranged in most of the imaging plane of the two-dimensional imaging element, an image shift amount is obtained from pixel signals of the focus detection pixels which are partially arranged and the focus detection of the phase difference method is performed.
However, according to the imaging plane phase difference method, since the rays of light which are received by the focus detection pixels which perform the focus detection and the rays of light which are received by the image pickup pixels which obtain the picked-up image differ, an influence on the focus detection signal by each aberration (spherical aberration, astigmatism, coma, or the like) of the photographing lens and that on the image pickup signal differ. Therefore, there is such a problem that a difference occurs between a detected in-focus position which is calculated from the focus detection signal and a most-preferable in-focus position of the image pickup signal.
The invention is made in consideration of the foregoing problem and it is an object of the invention to suppress a difference between a detected in-focus position which is calculated from a focus detection signal and a most-preferable in-focus position of an image pickup signal and to enable a focus detection to be performed at a high accuracy.